Motors and actuators are used in a wide variety of applications. Many applications, including robotics and active orthotics, require characteristics similar to human muscles. The characteristics include the ability to deliver high force at a relatively low speed and to allow free-movement when power is removed, thereby allowing a limb to swing freely during portions of the movement cycle. This may call for an actuator that can supply larger forces at slower speeds and smaller forces at higher speeds, or a variable ratio transmission (VRT) between the primary driver input and the output of an actuator.
VRTs have been conventionally implemented as Continuously Variable Transmissions (CVTs). The underlying principle of most previous CVTs is to change the ratio of one or more gears by changing the diameter of the gear, changing the place where a belt rides on a conical pulley, or by coupling forces between rotating disks with the radius of the intersection point varying based on the desired ratio. Prior art CVTs have drawbacks in efficiency and mechanical complexity.
Motors have been used in a variety of applications, but typically a single motor is directly or indirectly coupled to provide motion for each output direction. Use of a single motor limits the speed/torque range or requires the extra cost and complexity of a transmission between the motor and output. Thus, there is a need in the actuator field to create a new and useful actuator system that can supply larger forces at slower speeds and smaller forces at higher speeds, but that minimizes or avoids the disadvantages of the conventional CVTs. This invention provides such a new and useful actuator system.